The Koch Brothers, David and Charles Koch, both have a net worth of $43.8 billion, as of December 11, 2015. Combined, they have a total net worth of $87.6 billion.
The brothers run Koch Industries, a business inherited from their father, Fred Koch. Koch Industries, according to a 2010 Forbes survey, is the second largest privately held company in the United States. It was formerly only involved in oil refinery and chemical products, but today it has diversified its interests across many business areas. For example, Koch Industries now works with pollution control equipment, polymers, fibers, ranching, minerals and fertilizers and owns companies such as Stainmaster, Quilted Northern and Dixie Cup.